The present invention relates to a radio-frequency circuit for transmitting or radiating radio-frequency signals in frequency bands such as a microwave band and a milliwave band, and more particularly to a resonator for producing a resonance phenomenon at a specified design frequency (resonance frequency) in these bands.
In recent years, radio communication equipment with smaller size and higher functionality has been developed, which has allowed explosive growth of radio communication equipment typified by cell-phones and the like. In the future, it is predicted that there will be continuous demands for further downsizing of the radio communication equipment or each device for use in the radio communication equipment without damage on the functionality or the low cost thereof.
One of resonance circuit elements (resonators) for use in the radio-frequency circuit mounted on the radio equipment includes a radio-frequency circuit element using a slot circuit, a part of which is cut off from a ground conductor interconnection layer. For example, an oblong slot circuit can produce a resonance phenomenon at a half wave frequency equivalent to the distance between both the ends of the slot. Further, if a slot portion is disposed in a spiral fashion, the resonance phenomenon can be produced in lower frequency bands, i.e., against longer electromagnetic waves, without increase in space occupancy. For example, as shown in a cross sectional view in FIG. 14A and a top view in FIG. 14B, a resonator 500 has a slot circuit 505 formed in a square region, 2000 microns on a side, in a ground conductor layer 503 formed on the surface of a dielectric substrate 501 with a dielectric constant of 10 and a thickness of 600 microns, the slot circuit 505 being formed into a spiral shape with the turning number of 1.5 times, and the resonator 500 has a resonance frequency of 6.69 GHz.
Moreover, in an example shown in non patent document 1, two slot circuits in the spiral shape with the turning number of 2 to 4.5 times are disposed on the same plane in an axisymmetrical way and are further coupled in series to constitute a slot resonator which resonates at a half frequency of the respective spiral slot circuits and which is applied to part of a filter circuit. In this example, two spiral slot circuits are connected in series and their central portion is coupled with an input circuit so as to establish strong coupling.
[Non Patent Document 1]
“Miniaturized Slot-Line and Folded-Slot Band-Pass Filters”, P1595-P1598 of International Microwave Symposium Digest, MTT-S, 2003 IEEE